U.S. patent number 6,896,346 [Application Number 10/329,566] was granted by the patent office on 2005-05-24 for thermo-mechanical actuator drop-on-demand apparatus and method with multiple drop volumes.
This patent grant is currently assigned to Eastman Kodak Company. Invention is credited to John A. Lebens, Stephen F. Pond, David P. Trauernicht.
United States Patent |
6,896,346 |
Trauernicht , et
al. |
May 24, 2005 |
Thermo-mechanical actuator drop-on-demand apparatus and method with
multiple drop volumes
Abstract
An apparatus and method of operating a liquid drop emitter, such
as an ink jet device, for emitting liquid drops of different
volumes. The liquid drop emitter comprises a chamber, filled with a
liquid, having a nozzle for emitting drops of the liquid, a
thermo-mechanical actuator having a moveable portion within the
chamber for applying pressure to the liquid at the nozzle, and
apparatus adapted to apply heat pulses to the thermo-mechanical
actuator. The method for operating comprises applying a first heat
pulse having a first power P.sub.1, first pulse duration
.tau..sub.p1, and first energy E.sub.1 =P.sub.1.times..tau..sub.p1,
displacing the movable portion of the actuator so that a drop is
emitted having a first drop volume V.sub.d1, and traveling
substantially at the target velocity v.sub.0 ; and applying a
second heat pulse having a second power P.sub.2, second pulse
duration .tau..sub.p2, and second energy E.sub.2
=P.sub.2.times..tau..sub.p2, displacing the movable portion of the
actuator so that a drop is emitted having a second drop volume
V.sub.d2 and traveling substantially at the target velocity
v.sub.0, wherein V.sub.d2 >V.sub.d1, E.sub.2 >E.sub.1,
.tau..sub.p2 >.tau..sub.p1, and P.sub.2 <P.sub.1. An
alternate method for operating causes the emission of drops having
different volumes traveling at different velocities wherein all
velocities are within a pre-determined drop velocity range, v.sub.d
min to v.sub.d max. Further methods for operating an ink jet
printhead cause the emission of drops having different volumes and
velocities wherein the triggering of the drop emission is delayed
so as to result in synchronized arrival times at a print plane.
Inventors: |
Trauernicht; David P.
(Rochester, NY), Lebens; John A. (Rush, NY), Pond;
Stephen F. (Oakton, VA) |
Assignee: |
Eastman Kodak Company
(Rochester, NY)
|
Family
ID: |
32469034 |
Appl.
No.: |
10/329,566 |
Filed: |
December 26, 2002 |
Current U.S.
Class: |
347/9;
347/56 |
Current CPC
Class: |
B41J
2/04573 (20130101); B41J 2/04585 (20130101); B41J
2/04588 (20130101); B41J 2/0459 (20130101); B41J
2/04591 (20130101); B41J 2/04593 (20130101); B41J
2/14427 (20130101); B41J 2/1628 (20130101); B41J
2/1639 (20130101); B41J 2/1642 (20130101); B41J
2/1648 (20130101) |
Current International
Class: |
B41J
2/05 (20060101); B41J 2/14 (20060101); B41J
2/16 (20060101); B41J 029/38 (); B41J 002/05 () |
Field of
Search: |
;347/9,15,48,56,61 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
20330543 |
|
Jan 1990 |
|
JP |
|
WO 0214076 |
|
Feb 2002 |
|
WO |
|
Primary Examiner: Brooke; Michael S.
Attorney, Agent or Firm: Zimmerli; William R.
Claims
What is claimed is:
1. A method for operating a liquid drop emitter for emitting liquid
drops of substantially different volumes having substantially a
same target velocity v.sub.0, said liquid drop emitter comprising a
chamber, filled with a liquid, having a nozzle for emitting drops
of the liquid, a thermo-mechanical actuator having a moveable
portion within the chamber for applying pressure to the liquid at
the nozzle, and apparatus adapted to apply heat pulses to the
thermo-mechanical actuator, the method for operating comprising:
(a) applying a first heat pulse having a first power P.sub.1, first
pulse duration .tau..sub.p1, and first energy E.sub.1
=P.sub.1.times..tau..sub.p1, displacing the movable portion of the
actuator so that a drop is emitted having a first drop volume
V.sub.d1, and traveling substantially at the target velocity
v.sub.0 ; and (b) applying a second heat pulse having a second
power P.sub.2, second pulse duration .tau..sub.p2, and second
energy E.sub.2 =P.sub.2.times..tau..sub.p2, displacing the movable
portion of the actuator so that a drop is emitted having a second
drop volume V.sub.d2 and traveling substantially at the target
velocity v.sub.0, wherein V.sub.d2 >V.sub.d1, E.sub.2
>E.sub.1, .tau..sub.p2 >.tau..sub.p1 and P.sub.2
<P.sub.1.
2. The method of claim 1 wherein the liquid drop emitter is a
drop-on-demand ink jet printhead and the liquid is an ink for
printing image data.
3. The method of claim 1 wherein the thermo-mechanical actuator is
configured as a cantilever extending from a wall of the chamber and
having a free end adjacent the nozzle and moveable within the
chamber.
4. The method of claim 3 wherein the thermo-mechanical actuator
exhibits a damped mechanical resonance having a fundamental period
of .tau..sub.R and .tau..sub.p2 <1/4.tau..sub.R.
5. The method of claim 4 wherein the fundamental period
.tau..sub.R.ltoreq.20 microseconds and the second pulse duration
.tau..sub.p2.ltoreq.4 microseconds.
6. The method of claim 3 wherein the free end has a tip perimeter
having an arcuate shape and the chamber has an arcuate chamber
portion generally surrounding the free end and spaced away by a
clearance distance.
7. The method of claim 6 wherein the arcuate chamber portion
surrounds the tip perimeter for at least 180 degrees of arc.
8. The method of claim 6 wherein the clearance distance is 3
microns or less.
9. The method of claim 1 wherein the thermo-mechanical actuator
includes a deflector layer constructed of a deflector material
having a high coefficient of thermal expansion and a top layer,
attached to the deflector layer, constructed of a top material
having a low coefficient of thermal expansion.
10. The method of claim 9 wherein the deflector material is
electrically resistive and the apparatus adapted to apply a heat
pulse includes a resistive heater formed in the deflector
layer.
11. The method of claim 9 wherein the deflector material is
titanium aluminide.
12. A liquid drop emitter for emitting liquid drops of different
volumes having substantially a same target velocity v.sub.0, said
liquid drop emitter comprising: (a) a chamber, formed in a
substrate, filled with a liquid and having a nozzle for emitting
drops of the liquid and having an arcuate chamber portion; (b) a
thermo-mechanical actuator having a cantilevered element extending
from a wall of the chamber and having a free end with a tip
perimeter having an arcuate shape, the tip perimeter spaced away
from the arcuate chamber portion by a clearance distance and
moveable within the arcuate chamber portion for applying pressure
to the liquid at the nozzle; (c) apparatus adapted to apply heat
pulses to the thermo-mechanical actuator according to the method of
claim 1 wherein drops having substantially different volumes are
emitted at substantially the same target velocity v.sub.0.
13. A method for operating a liquid drop emitter for emitting
liquid drops of substantially different volumes having a drop
velocity that is within a predetermined drop velocity range,
v.sub.d min to v.sub.d max, said liquid drop emitter comprising a
chamber, filled with a liquid, having a nozzle for emitting drops
of the liquid, a thermo-mechanical actuator having a moveable
portion within the chamber for applying pressure to the liquid at
the nozzle, and apparatus adapted to apply heat pulses to the
thermo-mechanical actuator, the method for operating comprising:
(a) selecting a maximum drop velocity range, v.sub.d min to v.sub.d
max ; (a) applying a first heat pulse having a first power P.sub.1,
first pulse duration .tau..sub.p1, and first energy E.sub.1
=P.sub.1.times..tau..sub.p1, displacing the movable portion of the
actuator so that a drop is emitted having a first drop volume
V.sub.d1 and traveling at a first velocity, v.sub.1d, wherein
v.sub.d min.ltoreq.v.sub.1d <v.sub.d max ; and (c) applying a
second heat pulse having a second power P.sub.2, second pulse
duration .tau..sub.p2, and second energy E.sub.2
=P.sub.2.times..tau..sub.p2, displacing the movable portion of the
actuator so that a drop is emitted having a second drop volume
V.sub.d2 and traveling at a second velocity, v.sub.2d wherein
v.sub.1d <v.sub.2d.ltoreq.v.sub.d max, and wherein V.sub.d2 is
substantially greater than V.sub.d1, E.sub.2 >E.sub.1, and
.tau..sub.p2 >.tau..sub.p1.
14. The method of claim 13 wherein the liquid drop emitter is a
drop-on-demand ink jet printhead and the liquid is an ink for
printing image data.
15. The method of claim 14 wherein the drop velocity range, v.sub.d
min to v.sub.d max, is selected to achieve an image quality
characteristic.
16. The method of claim 13 wherein the thermo-mechanical actuator
is configured as a cantilever extending from a wall of the chamber
and having a free end adjacent the nozzle and moveable within the
chamber.
17. The method of claim 16 wherein the thermo-mechanical actuator
exhibits a damped mechanical resonance having a fundamental period
of .tau..sub.R and .tau..sub.p2 <1/4.tau..sub.R.
18. The method of claim 17 wherein the fundamental period
.tau..sub.R <20 microseconds and the second pulse duration
.tau..sub.p2.ltoreq.4 microseconds.
19. The method of claim 16 wherein the free end has a tip perimeter
having an arcuate shape and the chamber has an arcuate chamber
portion generally surrounding the free end and spaced away by a
clearance distance.
20. The method of claim 19 wherein the arcuate chamber portion
surrounds the tip perimeter for at least 180 degrees of arc.
21. The method of claim 19 wherein the clearance distance is 3
microns or less.
22. The method of claim 13 wherein the thermo-mechanical actuator
includes a deflector layer constructed of a deflector material
having a high coefficient of thermal expansion and a top layer,
attached to the deflector layer, constructed of a top material
having a low coefficient of thermal expansion.
23. The method of claim 22 wherein the deflector material is
electrically resistive and the apparatus adapted to apply a heat
pulse includes a resistive heater formed in the deflector
layer.
24. The method of claim 23 wherein the deflector material is
titanium aluminide.
25. The method of claim 13 wherein P.sub.2 =P.sub.1.
26. A liquid drop emitter for emitting liquid drops of
substantially different volumes having a drop velocity that is
within a predetermined drop velocity range, v.sub.d min to v.sub.d
max, said liquid drop emitter comprising: (a) a chamber, formed in
a substrate, filled with a liquid and having a nozzle for emitting
drops of the liquid and having an arcuate chamber portion; (b) a
thermo-mechanical actuator having a cantilevered element extending
a from a wall of the chamber and having a free end with a tip
perimeter having an arcuate shape, the tip perimeter spaced away
from the arcuate chamber portion by a clearance distance and
moveable within the arcuate chamber portion for applying pressure
to the liquid at the nozzle; (c) apparatus adapted to apply heat
pulses to the thermo-mechanical actuator according to the method of
claim 13 wherein drops having substantially different volumes are
emitted at drop velocities within the range v.sub.d min to v.sub.d
max.
27. A method for operating an ink jet printhead for emitting drops
having a plurality of volumes, V.sub.di, with associated
velocities, v.sub.id, and synchronized arrival times, t.sub.a, at a
print plane; said ink jet printhead comprising at least one chamber
having a nozzle for emitting drops of an ink filling the chamber, a
thermo-mechanical actuator for applying pressure to the ink,
apparatus adapted for applying heat pulses to the thermo-mechanical
actuator, a source of heat pulses, and controller apparatus adapted
for generating clock signals and determining the parameters of the
heat pulses, the method for operating comprising: (a) generating a
clock signal having a clock period and a clock period start, for
organizing the timing of the application of heat pulses so that at
least one drop, or no drop, is emitted per clock period; (b)
determining heat pulse parameters to be associated with each drop
volume V.sub.di having a velocity v.sub.id, said heat pulse
parameters comprising a pulse duration .tau..sub.pi, a time delay
t.sub.di, and a power P.sub.0, wherein the time delay t.sub.di is
selected to result in an arrival time of approximately t.sub.a at
the print plane; (c) receiving a command to emit a drop of volume
V.sub.di during a clock period; (d) waiting time t.sub.di from the
clock period start; and (e) applying a heat pulse having pulse
duration .tau..sub.pi and power P.sub.0 causing the emission of a
drop of volume V.sub.di and velocity v.sub.id that arrives at the
print plane at a time of approximately t.sub.a after the clock
period start.
28. The method of claim 27 wherein the thermo-mechanical actuator
is configured as a cantilever extending from a wall of the chamber
and having a free end adjacent the nozzle and moveable within the
chamber.
29. The method of claim 28 wherein the thermo-mechanical actuator
exhibits a damped mechanical resonance having a fundamental period
of .tau..sub.R and .tau..sub.pi <1/4.tau..sub.R.
30. The method of claim 27 wherein the free end has a tip perimeter
having an arcuate shape and the chamber has an arcuate chamber
portion generally surrounding the free end and spaced away by a
clearance distance.
31. The method of claim 27 wherein the thermo-mechanical actuator
includes a deflector layer constructed of a deflector material
having a high coefficient of thermal expansion and a top layer,
attached to the deflector layer, constructed of a top material
having a low coefficient of thermal expansion.
32. The method of claim 31 wherein the deflector material is
electrically resistive and the apparatus adapted to apply a heat
pulse includes a resistive heater formed in the deflector
layer.
33. The method of claim 23 wherein the deflector material is
titanium aluminide.
34. A method for operating an ink jet printhead for emitting drops
having a plurality of volumes, V.sub.di, with associated
velocities, v.sub.id, and synchronized arrival times, t.sub.a, at a
print plane; said ink jet printhead comprising at least one chamber
having a nozzle for emitting drops of an ink filling the chamber, a
thermo-mechanical actuator for applying pressure to the ink,
apparatus adapted for applying heat pulses to the thermo-mechanical
actuator, a source of heat pulses, and controller apparatus adapted
for generating clock signals and determining the parameters of the
heat pulses, the method for operating comprising: (a) generating a
clock signal having a clock period .tau..sub.c, a clock period
start, and a plurality of intermediate drop emission trigger times
tr.sub.j, tr.sub.j <.tau..sub.c, following the clock period
start for organizing the timing of the application of heat pulses
so that at least one drop, or no drop, is emitted per clock period;
(b) determining heat pulse parameters to be associated with each
drop volume V.sub.di having a velocity v.sub.id, said heat pulse
parameters comprising a pulse duration .tau..sub.pi, a drop
emission trigger time, tr.sub.i, and a power P.sub.0, wherein the
trigger time is selected to result in an arrival time of
approximately t.sub.a at the print plane; (c) receiving a command
to emit a drop of volume V.sub.di during a clock period; (d)
waiting until trigger time tr.sub.i ; and (e) applying a heat pulse
having pulse duration .tau..sub.pi and power P.sub.0 causing the
emission of a drop of volume V.sub.di and velocity v.sub.id that
arrives at the print plane at a time of approximately t.sub.a after
the clock period start.
35. The method of claim 34 wherein the thermo-mechanical actuator
is configured as a cantilever extending from a wall of the chamber
and having a free end adjacent the nozzle and moveable within the
chamber.
36. The method of claim 34 wherein the thermo-mechanical actuator
exhibits a damped mechanical resonance having a fundamental period
of .tau..sub.R and .tau..sub.pi <.tau..sub.R.
37. The method of claim 34 wherein the free end has a tip perimeter
having an arcuate shape and the chamber has an arcuate chamber
portion generally surrounding the free end and spaced away by a
clearance distance.
38. The method of claim 34 wherein the thermo-mechanical actuator
includes a deflector layer constructed of a deflector material
having a high coefficient of thermal expansion and a top layer,
attached to the deflector layer, constructed of a top material
having a low coefficient of thermal expansion.
39. The method of claim 38 wherein the deflector material is
electrically resistive and the apparatus adapted to apply a heat
pulse includes a resistive heater formed in the deflector
layer.
40. The method of claim 38 wherein the deflector material is
titanium aluminide.
Description
FIELD OF THE INVENTION
The present invention relates generally to drop-on-demand liquid
emission devices, and, more particularly, to ink jet devices which
employ thermo-mechanical actuators.
BACKGROUND OF THE INVENTION
Drop-on-demand (DOD) liquid emission devices have been known as ink
printing devices in ink jet printing systems for many years. Early
devices were based on piezoelectric actuators such as are disclosed
by Kyser et al., in U.S. Pat. No. 3,946,398 and Stemme in U.S. Pat.
No. 3,747,120. A currently popular form of ink jet printing,
thermal ink jet (or "bubble jet"), uses electroresistive heaters to
generate vapor bubbles which cause drop emission, as is discussed
by Hara et al., in U.S. Pat. No. 4,296,421.
Electroresistive heater actuators have manufacturing cost
advantages over piezoelectric actuators because they can be
fabricated using well developed microelectronic processes. On the
other hand, the thermal ink jet drop ejection mechanism requires
the ink to have a vaporizable component, and locally raises ink
temperatures well above the boiling point of this component. This
temperature exposure places severe limits on the formulation of
inks and other liquids that may be reliably emitted by thermal ink
jet devices. Piezo-electrically actuated devices do not impose such
severe limitations on the liquids that can be jetted because the
liquid is mechanically pressurized.
The availability, cost, and technical performance improvements that
have been realized by ink jet device suppliers have also engendered
interest in the devices for other applications requiring
micro-metering of liquids. These new applications include
dispensing specialized chemicals for micro analytic chemistry as
disclosed by Pease et al., in U.S. Pat. No. 5,599,695; dispensing
coating materials for electronic device manufacturing as disclosed
by Naka et al., in U.S. Pat. No. 5,902,648; and for dispensing
microdrops for medical inhalation therapy as disclosed by Psaros et
al., in U.S. Pat. No. 5,771,882. Devices and methods capable of
emitting, on demand, micron-sized drops of a broad range of liquids
are needed for highest quality image printing, but also for
emerging applications where liquid dispensing requires
mono-dispersion of ultra small drops, accurate placement and
timing, and minute increments.
A low cost approach to micro drop emission is needed that can be
used with a broad range of liquid formulations. Apparatus and
methods are needed that combine the advantages of microelectronic
fabrication used for thermal ink jet with the liquid composition
latitude available to piezo-electro-mechanical devices.
A DOD ink jet device that uses a thermo-mechanical actuator was
disclosed by T. Kitahara in JP 2,030,543, filed Jul. 21, 1988. The
actuator is configured as a bi-layer cantilever moveable within an
ink jet chamber. The beam is heated by a resistor causing it to
bend due to a mismatch in thermal expansion of the layers. The free
end of the beam moves to pressurize the ink at the nozzle causing
drop emission. Recently, disclosures of a similar thermo-mechanical
DOD ink jet configuration have been made by K. Silverbrook in U.S.
Pat. Nos. 6,067,797; 6,234,609; and 6,239,821. Methods of
manufacturing thermo-mechanical ink jet devices using
microelectronic processes have been disclosed by K. Silverbrook in
U.S. Pat. Nos. 6,254,793 and 6,274,056.
Thermo-mechanically actuated drop emitters are promising as low
cost devices which can be mass produced using microelectronic
materials and equipment and which allow operation with liquids that
would be unreliable in a thermal ink jet device. In addition,
apparatus and methods of operating liquid drop emitters so as to
usefully generate drops having substantially different drop volumes
would be highly desirable. Such apparatus and methods would allow a
single drop emitter to provide different levels of the liquid per
drop firing cycle. In ink jet printing this capability may be used
to generate multiple image gray levels while preserving the
printing speed associated with binary printing. The gray level
printing capability of a single ink drop emitter may allow a
printing system to be designed with fewer jets to achieve lower
overall system cost or, alternatively, may be configured to achieve
higher net printing speeds of gray level images at apparatus costs
similar to a binary level printing system.
Some methods of emitting different ink drop volumes from
drop-on-demand ink jet printheads have been disclosed and used
previously. Use of fluid resonances for such purpose is known for
piezoelectric drop-on-demand ink jet devices. In these known
methods, the resonance of the ink meniscus at the nozzle, driven by
surface tension effects, or the Helmholtz resonance of the ink
chamber, driven by compliance effects, is used to change the volume
or number of emitted drops. Tence et al. in U.S. Pat. No. 5,689,291
employ waveforms that drive piezoelectric transducers with spectral
energy concentrations at frequencies associated with modal
resonances of ink in the ink jet printhead orifices. Exciting
different resonance modes of the ink meniscus causes the emission
of different drop sizes.
DeBonte et al., in U.S. Pat. No. 5,202,659 disclose a method of
operating a piezoelectric printhead using the dominant resonant
frequency of the ink jet apparatus. This dominant resonance is
described as the Helmholtz resonance of an individual jet chamber,
which is excited by actuating the piezo transducer to first expand
the jet chamber, waiting the resonance period, and then contracting
the chamber to reinforce this resonance. This excitation process is
repeated for multiple cycles to generate multiple merging drops for
printing spots having different sizes.
Paton et al., in U.S. Pat. No. 5,361,084 disclose a method of
multi-tone printing using a piezoelectric DOD printhead having
elongated ink chambers and sidewall actuators, wherein an
individual jet is excited using a packet of pulses so as to excite
a longitudinal acoustic resonance in the jet channel that causes
the emission of a number of discrete drops. Lee et al., in U.S.
Pat. No. 4,513,299 disclose a similar use of acoustic resonance of
the ink channels of a piezoelectric ink jet printhead.
The piezoelectric transducer used in a piezoelectric printhead may
be driven to both compress and expand the ink fluid chamber,
thereby allowing the ink meniscus at the nozzle to be pushed out or
pulled inward. A variation in emitted drop volume may be achieved
by manipulating the meniscus position and velocity by a sequence of
compressive and expansive electrical pulses. Apparatus and methods
of operating a piezoelectric drop-on-demand inkjet printhead in
this fashion have been disclosed by S. Sakai in U.S. Pat. No.
5,933,168 and by Horii, et al., in U.S. Pat. No. 6,095,630.
Apparatus and methods of operating a thermal ink jet drop-on-demand
printhead to create multiple drop volumes also have been disclosed.
For example, Bohorquez, et al., in U.S. Pat. No. 5,726,690,
describe a method of operating a thermal inkjet printhead that
includes changing the pulse width of the driving electrical pulse,
increasing the applied energy and thereby resulting in the emission
of larger drops for larger energy inputs. Drop volumes that range
in magnitude approximately 16% are disclosed.
Larger drop volume changes are reported for thermal ink jet
apparatus and methods that are configured so that different areas
of heater resistor can be energized. For example, Ishinaga, et al.,
in U.S. Pat. No. 5,880,762 discloses an apparatus having a
plurality of heat generating resistors per ink nozzle chamber. The
plurality of heat generating resistors are driven independently to
cause the emission of several different drop volumes. J. Wade, in
U.S. Pat. No. 6,318,847, discloses a segmented area heater resistor
configuration that may be energized to generate a range of vapor
bubble volumes causing the emission of differently sized drops.
Thermo-mechanical actuators are substantially smaller in scale than
the piezoelectric actuators used in ink jet printheads and have
mechanically different resonant behaviors. Thermo-mechanical
actuators are more complex to fabricate than thermal ink jet heater
resistors and, therefore, more difficult to construct in a
multiple-actuator per jet configuration in analogous fashion to the
disclosed thermal ink jet apparatus above noted. Apparatus and
methods that generate variable drop volumes are needed which are
adapted to the unique physical configurations, behaviors and
capabilities of thermo-mechanical actuators.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a
thermo-mechanical drop emitter and method of operating same to emit
drops having substantially different volumes and substantially the
same velocity.
It is also an object of the present invention to provide a
thermo-mechanical drop emitter and method of operating same to emit
drops having substantially different volumes and velocities within
a pre-selected range.
It is also an object of the present invention to provide a method
of operating an ink jet printhead to emit drops having
substantially different volumes and velocities, the emissions of
which are time-delayed so as to synchronize drop arrival times at a
print plane.
The foregoing and numerous other features, objects and advantages
of the present invention will become readily apparent upon a review
of the detailed description, claims and drawings set forth herein.
These features, objects and advantages are accomplished by
operating a liquid drop emitter, such as an ink jet device, for
emitting liquid drops of different volumes. The liquid drop emitter
comprises a chamber, filled with a liquid, having a nozzle for
emitting drops of the liquid, a thermo-mechanical actuator having a
moveable portion within the chamber for applying pressure to the
liquid at the nozzle, and apparatus adapted to apply heat pulses to
the thermo-mechanical actuator. The method for operating comprises
applying a first heat pulse having a first power P.sub.1, first
pulse duration .tau..sub.p1, and first energy E.sub.1
=P.sub.1.times..tau..sub.p1, displacing the movable portion of the
actuator so that a drop is emitted having a first drop volume
V.sub.d1 and traveling substantially at a target velocity v.sub.0 ;
and applying a second heat pulse having a second power P.sub.2,
second pulse duration .tau..sub.p2, and second energy E.sub.2
=P.sub.2.times..tau..sub.p2, displacing the movable portion of the
actuator so that a drop is emitted having a second drop volume
V.sub.d2 and traveling substantially at the target velocity
v.sub.0, wherein V.sub.d2 >V.sub.d1, E.sub.2 >E.sub.1,
.tau..sub.p2 >.tau..sub.p1 and P.sub.2 <P.sub.1. Alternate
methods for operating cause the emission of drops having
substantially different volumes traveling at substantially
different velocities wherein all velocities are within a
pre-selected velocity range, v.sub.min to v.sub.max.
The present invention is particularly useful for operating liquid
drop emitters for DOD ink jet printing. Further methods for
operating an ink jet printhead cause the emission of drops having
different volumes and velocities wherein the triggering of the drop
emission is delayed so as to result in synchronized arrival times
at a print plane.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of an ink jet system according
to the present invention;
FIG. 2 is a plan view of an array of ink jet units or liquid drop
emitter units according to the present invention;
FIGS. 3(a) and 3(b) are enlarged plan views of an individual ink
jet unit illustrated in FIG. 2;
FIGS. 4(a)-4(c) are side views of an individual ink jet unit as
illustrated in FIG. 3(a) illustrating the movement of the
thermo-mechanical actuator to emit drops;
FIG. 5 is a perspective view of a step of the manufacturing method
according to the present inventions wherein a bottom layer is
formed;
FIG. 6 is a perspective view of a step of the manufacturing method
according to the present inventions wherein a deflector layer is
formed;
FIG. 7 is a perspective view of a step of the manufacturing method
according to the present inventions wherein a top layer is
formed;
FIG. 8 is a perspective view of a step of the manufacturing method
according to the present inventions wherein a sacrificial layer is
formed;
FIG. 9 is a perspective view of a step of the manufacturing method
according to the present inventions wherein a structure layer is
formed;
FIGS. 10(a)-10(c) are side views of final stages of the
manufacturing method according to the present inventions wherein a
liquid chamber is created by removing sacrificial material, and the
thermo-mechanical actuator is released and the fluid pathway
completed by removing substrate material beneath the moveable and
free edge areas;
FIG. 11 reports experimental data showing the relationship of drop
volume, drop velocity and input heat energy for a constant heat
pulse duration;
FIG. 12 reports experimental data showing the relationship of drop
volume, input heat energy and heat pulse duration for drops having
substantially the same velocity;
FIG. 13 illustrates geometrical parameters important to the
resonant oscillation behavior of a cantilevered thermo-mechanical
actuator and reports experimental results for the fundamental
resonant periods and damping time constants for several
experimental thermo-mechanical actuator configurations;
FIG. 14 illustrates damped resonant oscillation of a
thermo-mechanical actuator according to the present inventions;
FIG. 15 illustrates the effect of varying drop velocity on drop
placement at a print plane.
FIGS. 16(a) and 16(b) illustrate the heat pulse parameters
associated with two alternative methods of operating according to
the present inventions;
FIG. 17 illustrates the heat pulse parameters associated with some
alternative methods of operating an ink jet printhead according to
the present inventions;
FIG. 18 illustrates the heat pulse parameters associated with other
preferred methods of operating an ink jet printhead according to
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention.
As described in detail herein below, the present invention provides
an apparatus and method of operating a drop-on-demand liquid
emission device. The most familiar of such devices are used as
printheads in ink jet printing systems. Many other applications are
emerging which make use of devices similar to ink jet printheads,
however which emit liquids other than inks that need to be finely
metered and deposited with high spatial precision. The terms ink
jet and liquid drop emitter will be used herein interchangeably.
The inventions described below provide apparatus and methods for
operating drop emitters based on thermo-mechanical actuators so as
to usefully emit drops having substantially different volumes.
Turning first to FIG. 1, there is shown a schematic representation
of an ink jet printing system that may use an apparatus
manufactured by methods according to the present invention. The
system includes an image data source 400 that provides signals
received by controller 300 as commands to print drops. Controller
300 outputs signals to a source of electrical pulses 200. Pulse
source 200, in turn, generates an electrical voltage signal
composed of electrical energy pulses that are applied to
electrically resistive means associated with each thermo-mechanical
actuator 15 within ink jet printhead 100. The electrical energy
pulses cause a thermo-mechanical actuator 15 to bend rapidly,
pressurizing ink 60 located at nozzle 30, and emitting an ink drop
50 that lands on receiver or print plane 500.
FIG. 2 shows a plan view of a portion of ink jet printhead 100. An
array of thermally actuated ink jet units 110 is shown having
nozzles 30 centrally aligned, and upper ink chambers 11 outwardly
bounded by chamber structures 33, interdigitated in two rows. The
ink jet units 110 are formed on and in a substrate 10 using
microelectronic fabrication methods as described herein.
Each drop emitter unit 110 has associated electrical lead contacts
42, 44 that are formed with, or are electrically connected to, a
u-shaped electrically resistive heater 27, shown in phantom view in
FIG. 2. In the illustrated embodiment, the resistor 27 is formed in
a deflector layer of thermo-mechanical actuator 15 and participates
in the thermo-mechanical effects. Element 80 of the printhead 100
is a mounting structure that provides a mounting surface for
microelectronic substrate 10 and other means for interconnecting
the liquid supply, electrical signals, and mechanical interface
features.
FIG. 3a illustrates a plan view of a single drop emitter unit 10
and a second plan view FIG. 3b with the liquid chamber structure
33, enclosing the upper ink chamber 11 and including nozzle 30,
removed. Upper ink chamber 11 has an arcuate portion 36 that
generally surrounds the arcuate free end 28 of the
thermo-mechanical actuator 15.
Thermo-mechanical actuator 15, shown in phantom in FIG. 3a can be
seen with solid lines in FIG. 3b. The cantilevered element. 20 of
thermo-mechanical actuator 15 extends from edge 14 of lower ink
chamber 12 that is formed in substrate 10. Cantilevered element
portion 17 is bonded to substrate 10 and anchors the
cantilever.
The cantilevered element 20 of the actuator has the shape of a
paddle, an extended flat shaft ending with a disc of larger
diameter than the shaft width. This shape is merely illustrative of
cantilever actuators that can be used. Many other shapes are
applicable. The paddle shape aligns the nozzle 30 with the center
of the cantilever free end 28. The lower liquid chamber 12 has a
curved wall portion 16 that conforms to the arcuate shaped portion
34 of the actuator free end 28, spaced away to provide a clearance
gap 13 for actuator movement. The arcuate portion 34 of free end 28
and the arcuate portions of the upper and lower liquid chambers 36
and 16, are illustrated to extend for an angular amount .THETA.,
wherein .THETA. is 180 degrees or more. The opposing free edges 19
of the thermo-mechanical actuator, together with free end 28,
define an outline of the moveable portion of the thermo-mechanical
actuator.
FIG. 3b illustrates schematically the attachment of electrical
pulse source 200 to the electrically resistive heater 27 at
interconnect terminals 42 and 44. Voltage differences are applied
to voltage terminals 42 and 44 to cause resistance heating via
u-shaped resistor 27. This is generally indicated by an arrow
showing a current I. In the plan views of FIG. 3, the actuator free
end moves toward the viewer when pulsed and drops are emitted
toward the viewer from the nozzle 30 in liquid chamber structure
28. This geometry of actuation and drop emission is called a "roof
shooter" in many ink jet disclosures.
FIG. 4 illustrates in side view a cantilevered element 20 according
to a preferred embodiment of the present invention. In FIG. 4a the
cantilevered element 20 is in a first position and in FIG. 4b it is
shown deflected upward to a second position. In FIG. 4c the
cantilevered element is shown in a recoiled, downwardly deflected
position. Cantilevered element 20 is anchored to substrate 10 that
serves as a base element for the thermo-mechanical actuator.
Cantilevered element 20 extends from wall edge 14 of substrate base
element 10.
Cantilevered element 20 is constructed of several layers. Layer 24
is the deflector layer that causes the upward deflection when it is
thermally elongated with respect to other layers in the
cantilevered element. The deflector material is chosen to have a
high coefficient of thermal expansion. Further, in the illustrated
configuration, the deflector material is electrically resistive and
a portion is patterned into a heater resistor for receiving
electrical pulses to heat the thermo-mechanical actuator.
Electrically resistive materials are generally susceptible to
chemical interaction with components or impurities in a working
fluid.
Top layer 26 is formed with a top material having a substantially
lower coefficient of thermal expansion than the deflector material
and has a layer thickness that is on the order of, or larger than,
the deflector layer thickness. Top layer 26 in FIG. 4 does not
expand as much as the deflector layer when heated thereby
constraining the deflector layer from simply elongating and causing
the overall cantilevered element 20 to bend upward, away from
deflector layer 24. For embodiments wherein the deflector material
is electrically resistive and formed with a heater resistor, the
top layer material is a dielectric. The top layer material is also
chosen to be chemically inert to the working fluid.
Bottom layer 22 is formed of a bottom material that is chemically
inert to the working fluid being used with the device, for example,
an ink for ink jet printing. It protects the lower surface of the
deflector material from chemical interaction. In addition, the
bottom material serves as an etch stop during a manufacturing
process step described hereinbelow in which substrate material is
removed beneath the thermo-mechanical actuator.
The terms "top" and "bottom" are chosen to reference layers with
respect to position relative to the substrate. These layers also
play a role in determining which direction the deflector layer
causes the thermo-mechanical actuator to bend. If both layers were
formed of the same materials and of equal thickness, the actuator
might not bend at all. The deflector layer will be caused to bend
towards whichever layer, top or bottom, is more constraining as a
result of its thickness, thermal expansion coefficient and Young's
modulus. The biasing of the movement direction is readily achieved
by making the layer that is toward the desired direction
substantially thicker than the away layer.
When used as actuators in drop emitters the bending response of the
cantilevered element 20 must be rapid enough to sufficiently
pressurize the liquid at the nozzle. Typically, electrically
resistive heating apparatus is adapted to apply heat pulses and
electrical pulses with duration of less than 10 .mu.secs and,
preferably, with duration less than 4 .mu.secs.
In an operating emitter of the cantilevered element type
illustrated, the quiescent first position may be a partially bent
condition of the cantilevered element 20 rather than the horizontal
condition illustrated FIGS. 4a and 10c. The actuator may be bent
upward or downward at room temperature because of internal stresses
that remain after one or more microelectronic deposition or curing
processes. The device may be operated at an elevated temperature
for various purposes, including thermal management design and ink
property control. If so, the first position may be substantially
bent.
For the purposes of the description of the present inventions
herein, the cantilevered element will be said to be quiescent or in
its first position when the free end is not significantly changing
in deflected position. For ease of understanding, the first
position is depicted as horizontal in FIGS. 4a and 10c. However,
operation of thermo-mechanical actuators about a bent first
position are known and anticipated by the inventors of the present
invention and are fully within the scope of the present
inventions.
FIGS. 5 through 10(c) illustrate methods of manufacturing applied
to an ink jet device or other liquid drop emitter having a
cantilevered element thermo-mechanical actuator, as illustrated in
FIGS. 3 and 4. FIG. 5 illustrates a perspective view of a single
cantilevered element at an initial stage of a manufacturing
process. Bottom layer 22 has been formed of a bottom material on
substrate 10. The bottom material has been removed in a bottom
layer pattern so that the substrate is now exposed in some areas.
These exposed areas of the substrate will eventually be removed to
form portions of the lower liquid chamber 12 and the clearance gap
13 illustrated in FIG. 3b. The large rectangular areas of substrate
exposure are refill areas 35, which are sized to provide adequate
upper chamber refill flow during rapid liquid drop emission, thus
allowing a tightly fitting clearance gap 13 to improve drop
ejection efficiency without compromising refill. The moveable
portion of the bottom layer 22 has opposing free edges 19. The
substrate 10 is also exposed in free edge area 18 adjacent the
arcuate edge 34 of the free end.
The bottom material for the cantilevered element thermo-mechanical
actuator is deposited as a thin layer so to minimize its impedance
of the upward deflection of the finished actuator. A chemically
inert, pinhole free material is preferred so as to provide chemical
and electrical protection of the deflector material that will be
formed on the bottom layer. A preferred method of the present
inventions is to use silicon wafer as the substrate material and
then a wet oxidation process to grow a thin layer of silicon
dioxide. Alternatively, a high temperature chemical vapor
deposition of a silicon oxide, nitride or carbon film may be used
to form a thin, pinhole free dielectric layer with properties that
are chemically inert to the working fluid.
FIG. 6 illustrates the addition of a deflector layer 24 over the
previously deposited bottom layer. Deflector material is removed in
a deflector layer pattern. In the illustrated configuration, the
deflector layer is comprised of an electrically resistive deflector
material, a portion of which is patterned into a u-shaped heater
resister 27 which can be addressed by input leads 42 and 44.
Deflector material is removed so that it does not overlap the
bottom layer material. In the design illustrated in FIG. 6, the
deflector material is removed well back from edges 19 of bottom
layer 22. Alternatively, the deflector layer and the bottom layer
could be patterned together using the bottom layer pattern so that
both layers coincided at free edges 19. A subsequent patterning of
the deflector layer only would then be needed to introduce any
unique features such as the resistor and addressing leads.
The deflector material is selected to have a high coefficient of
thermal expansion, for example, a metal. In addition, for the
examples illustrated herein, the deflector material is electrically
resistive and used to form a heater resistor. Nichrome (NiCr) is a
well known material that could be used as a deflector material. A
60% copper, 40% nickel alloy, cupronickel, and titanium nitride are
disclosed in K. Silverbrook U.S. Pat. Nos. 6,254,793 and
6,274,056.
An especially efficient and preferred bending material is
intermetallic titanium aluminide (TiAl), disclosed in co-pending
U.S. patent application Ser. No. 09/726,945 filed Nov. 30, 2000,
for "Thermal Actuator", assigned to the assignee of the present
invention. TiAl material may be formed by RF or DC magnetron
sputtering in argon gas. It has been found that desirable TiAl
films are predominantly disordered face-centered cubic (fcc) in
crystalline structure and have a stoichiometry of Al.sub.4-x
Ti.sub.x, where 0.6.ltoreq.x.ltoreq.1.4. Titanium aluminide may be
pattern etched with a standard chlorine-based dry etching system
commonly used in microelectronic device fabrication for aluminum
etching.
If the resistivity of the deflector material is in an appropriate
range, then a portion of the deflector layer can be patterned as a
resistor and used to introduce heat pulses to the thermo-mechanical
actuator. Alternatively, a separate electrical resistor layer can
be added or heat energy can be coupled to the actuator by other
means such as light energy or inductively coupled electrical
energy. The titanium aluminide material preferred in the present
inventions has a resistivity of .about.160 .mu.ohm-cm, which is a
reasonable resistivity for a heater resistor that could be driven
by integrated circuit transistors. Typical thicknesses, h.sub.d,
for the deflector layer are 0.5 .mu.m to 2 .mu.m.
FIG. 7 illustrates in perspective view the addition of a top layer
26 formed over the deflector layer 24, bottom layer 22, and
substrate 10. The top layer 26 is removed in a top layer pattern
that generally leaves top layer material covering the deflector
material in the moveable area of the cantilevered element. The top
layer as illustrated in FIG. 7 performs two main functions, it
protects the deflector material from chemical interaction with the
working fluid, and it biases the deflection of cantilevered element
20 towards itself.
A typical dielectric material used for the top material is silicon
dioxide or silicon nitride. Many other dielectrics may be used. In
the configuration of FIG. 7 wherein the top layer is relatively
thick, oxides and nitrides deposited by low temperature CVD
processes will provide substantial chemical interaction protection
for the deflector layer. The top layer pattern leaves top material
covering the free edges of the deflector layer so as to provide
chemical and electrical passivation. Further, the top material free
edges may underlap, overlap or be coincident with bottom layer free
edges 19. An underlapping condition is illustrated in FIG. 7. If
the top material is allowed to overlap the bottom material into
free edge area 18 on substrate 10, it cannot be allowed to
completely cover free edge area 18. Some portion of free edge area
18 adjacent the arcuate free edge 34 of the free end 28 of
cantilevered element 20 must remain so that a subsequent process
step of removing the substrate beneath free edge area 18 is
effective in releasing the moveable portion of the cantilevered
clement 20 from attachment to the substrate.
The patterning of top layer 26 completes the construction of the
cantilevered element 20 for the liquid drop emitter 110 being
discussed. Other layers may be added for other purposes, for
example a separate layer and insulator to form a resistive heater,
instead of using the deflector material for this function. Also,
the top, deflector and bottom layers may be comprised of sub-layers
or layers with graded material properties. Such additional layers
and features are known and comprehended by the inventors as being
within the scope of the methods of manufacture of the present
inventions.
FIG. 8 shows the addition of a sacrificial layer 29 formed of a
sacrificial material and removed in a sacrificial layer pattern.
The sacrificial layer pattern leaves the sacrificial material
formed into the shape of the interior of an upper liquid chamber 11
of a liquid drop emitter. For a generalized liquid control device
concept, this chamber space can be understood as a movement volume
for the thermo-mechanical actuator. By movement volume it is meant
the space into which the moveable portion of the thermo-mechanical
actuator can travel freely without being impeded by structural
elements.
The sacrificial material is intended as a temporary form whose
outer surface shape will become the inner surface shape of the
structure layer that is to be next added. In addition the
sacrificial material must be able to fully conform to the
underlying layered structure of the cantilevered element including
making good contact with the free edge area 18 on substrate 10.
Any material that can be selectively removed with respect to the
adjacent materials, fully conforms to the underlying topography
down to the free edge area 18, and remains smooth and planar after
patterning and curing is a candidate for constructing sacrificial
layer 29.
FIG. 9 illustrates a patterned structure layer 33 formed by a
structure material deposited over the sacrificial layer and other
exposed layers on the substrate. Structure material is then removed
according to a structure layer pattern resulting in the drop
emitter liquid chamber 33 with walls, cover and nozzle 30, and
arcuate wall portion 36 illustrated in FIG. 9. In generic liquid
control device terms, the patterned structure layer 33 contains a
movement volume 11 and provides a structure opening 30 that
communicates with the sacrificial material still occupying the
movement volume space. Electrical leads 42 and 44 are exposed for
electrical attachment to an electrical pulse source.
Suitable structure materials include plasma deposited silicon
oxides or nitrides. The structure material must conform to the
rather deep topography of the completed sacrificial layer 29. The
sacrificial layer ranges in height above the substrate from
.about.1 .mu.m in the area around electrical leads 42, 44 up to 5
.mu.m-15 .mu.m at the upper surface 31 of the movement volume 11
(see FIG. 8). The structure material must also be chemically inert
to the working fluid and mechanically strong and durable enough to
withstand drop ejection pressure pulses and some mechanical wiping
for printhead maintenance purposes.
FIGS. 10(a)-10(c) show side views of the device through a section
indicated as A--A in FIG. 9. In FIG. 10a the sacrificial layer 29
is enclosed within the drop emitter chamber walls 33 except for
nozzle opening 30. Also illustrated in FIG. 10a, the substrate 10
is intact. The substrate is covered by sacrificial material in gap
area 13 immediately above free edge area 18 adjacent the free edges
of the cantilevered element. For the configuration illustrated in
FIG. 10, the most outer edge of the moveable portion of the
cantilevered element aligns with the free edges 19 and 34 of bottom
layer 22 as illustrated in FIGS. 5-7.
In FIG. 10b, substrate 10 is removed beneath the cantilevered
element 20, the liquid chamber areas around and beside the
cantilevered element 20 and the free edge area 18. This removal may
be accomplished by an anisotropic etching process such as reactive
ion etching for the case where the substrate used is single crystal
silicon. For constructing a thermo-mechanical actuator alone, the
sacrificial structure and liquid chamber steps are not needed and
this step of etching away substrate 10 may be used to release
cantilevered element 20 from attachment to substrate 10.
Removal of the substrate material, in addition to releasing the
moveable portion of the thermo-mechanical actuator, opens a pathway
for liquid to enter the liquid emission device from the substrate.
At the fabrication stage illustrated in FIG. 10b, liquid entering
from lower liquid chamber volume 12 may touch the bottom layer 22
of the cantilevered element 20, the sacrificial material in gap
area 13, and the sacrificial material in the large refill areas 35
(see FIGS. 5-7) flanking the cantilevered element, not visible in
this A--A cross sectional view lengthwise through the cantilevered
element. The refill areas are sized to provide rapid refill of
upper liquid chamber 11 following drop ejection for liquid drop
emitter devices.
In FIG. 10c the sacrificial material layer 29 has been removed
using a penetrating process such as dry etching using oxygen and
fluorine sources. The etchant gasses enter via the nozzle 30 and
from the newly opened fluid supply chamber area 12, etched
previously from the backside of substrate 10. This step removes the
sacrificial material from the movement volume of the device,
allowing the cantilevered element 20 to move freely and completes
the fabrication of a liquid drop emitter structure.
The process steps of removing the substrate material and removing
the sacrificial material illustrated in FIG. 10 may be performed in
either order. It may be beneficial to remove the substrate material
and then singulate individual devices leaving the sacrificial
material intact to protect the movable portion of the
thermo-mechanical actuator and prevent particles from entering the
movement volume. A drop emitter device may be mechanically mounted,
and interconnected electrically and fluidically with a protective
filter, in a less clean environment if the sacrificial material is
left inside the device until a later, final step in the overall
manufacturing workflow. However, it is also feasible to remove the
sacrificial material first when the substrate is still whole. This
process latter order offers the productivity advantage of
performing the sacrificial material etch on a wafer level set of
devices, instead of individually.
FIGS. 5 through 10c illustrate a preferred fabrication sequence.
However, many other construction approaches may be followed using
well known microelectronic fabrication processes and materials. For
the purposes of the present invention, any fabrication approach
which results in a cantilevered element including a deflector layer
24 and a top layer 26 may be followed. Further, in the illustrated
sequence of FIGS. 5 through 10c, the liquid chamber 33 and nozzle
30 of a liquid drop emitter were formed in situ on substrate 10.
Alternatively a thermo-mechanical actuator could be constructed
separately and bonded to a liquid chamber component to form a
liquid drop emitter.
It has been discovered by the inventors of the present inventions
that the volume or size of the liquid drops emitted by a
thermo-mechanically actuated liquid drop emitter may be varied by
changing the parameters of the heat pulses applied to the actuator.
Returning to FIGS. 3 and 4, it may be understood that when an
appropriate rapid heat pulse is applied to the cantilevered element
20, the free end 28 is caused to move rapidly towards nozzle 30,
accelerating a fluid volume generally having the area of the free
end 28 times the amount of free end displacement, y(L). The volume
of liquid emitted is roughly proportional to the amount of fluid
displaced by the moving cantilevered element.
The free end 28 of cantilevered element 20 is deflected an amount
y(L) by thermo-mechanical expansion effects in the various layers,
caused by raising the temperature of one or more layers an amount
.DELTA.T above ambient. That is, a simple first order equilibrium
analysis will show that:
where c is a thermo-mechanical structure factor which depends on
the Young's modulus, the coefficient of thermal expansion, the
thickness, and the Poisson's ratio of each of the layers of the
cantilevered element which is heated. It is not necessary to
examine the details of the somewhat complex thermo-mechanical
structure factor to understand the present inventions. The quantity
(c.DELTA.T) in Equation 1 is termed the thermal moment of the
multi-layered structure.
The temperature of the thermo-mechanical actuator is raised by a
heat pulse of energy E, applied at a power level P for a pulse time
duration .tau..sub.p.
To first order, the temperature rise, .DELTA.T, is then:
##EQU1##
where m.sub.eff is the effective mass and C.sub.eff is the
effective heat capacity of the heated portion of the
thermo-mechanical actuator.
Thus, a first order equilibrium analysis of the relationship
between the deflection of the free end 28 of the cantilevered
element, which largely determines emitted drop volume, yields the
following: ##EQU2##
From Equation 4, the emitted drop volume may be anticipated to
increase proportionately to an increase in applied energy E. If a
constant input power, P.sub.0, is utilized, then Equation 4 also
implies that the drop volume will increase proportionately to an
increase in pulse time duration .tau..sub.p.
FIG. 11 shows experimental data 250 for drop volume emitted as a
function of applied input energy using a constant pulse time
duration, .tau..sub.p =2 .mu.sec. The data plotted in FIG. 11 were
collected for a representative drop emitter filled with water and
configured as illustrated in FIGS. 3 and 4. The cantilevered
element 20 length L was 90 .mu.m, the width of the rectangular
portion of the cantilever and the diameter of the semi-circular
free end 28 were both 30 .mu.m. The nozzle 30 diameter was 14
.mu.m. The resistance of a heater resistor 27 formed in a deflector
layer 24 was 26 ohms. Individual data points are marked by dots
along plot 250. Individual data points are also labeled with the
drop velocity observed for each drop volume.
It may be seen from FIG. 11 that over a certain input energy range,
.about.3.6 .mu.J-4.3 .mu.J, the emitted drop volume is
approximately proportional to the input energy. The drop velocity
also varied in this experiment from a low of .about.1.3
meters/sec., up to 8.9 m/sec. Drop emission exhibits a threshold
effect in that no drops are emitted until a certain threshold is
reached, approximately 3.6 .mu.J for the experimental conditions
reported in FIG. 11. The large amount of threshold energy is needed
to overcome the effects of compliance in the drop emitter structure
and to overcome fluid mechanical forces arising from surface
tension and fluid viscosity, which resist the formation of a liquid
jet at the nozzle.
An upper limit on the amount of input energy that may be usefully
applied is imposed by certain high temperature failure modes. It
was found that for larger input energies than the 4.6 .mu.J point
plotted in FIG. 11 still larger volume drops were emitted but at
erratic drop velocities. Vapor bubble formation was observed near
the hottest locations on the thermo-mechanical actuator for these
larger input energy pulses, E>4.6 .mu.J. Vapor bubble formation
and collapse is undesirable because it introduces unpredictable
pressure impulses or may cause cavitation damage to the
thermo-mechanical actuator or a build-up of kogated ink
materials.
Many applications of liquid drop emitters, for example ink jet
printing, fire drops across a spacing gap distance, G.sub.p, to a
predetermined receiver location, i.e. a pixel location in a raster
image. In addition, for many of these applications, the liquid drop
emitter and the receiver are moved with respect to each other by a
carriage mechanism at a relative velocity, v.sub.c, so that drops
may be deposited at different locations in a time efficient
fashion. A predictable drop velocity, v.sub.d0, is therefore
necessary in order to direct drops to the intended location. If the
drop velocity varies, then the flying time from the nozzle to the
receiver plane, G.sub.p /v.sub.d0, will vary. If the flying time
varies, then the distance traveled in the direction of the relative
motion, d.sub.c, will also vary accordingly: ##EQU3##
Some amount of variation in d.sub.c, i.e. some drop placement error
relative to predetermined locations such as image pixel rasters,
due to drop velocity variation, may be tolerable depending on the
specific system application of the drop emitter. In ink jet
printing such drop placement errors may affect the perceived
sharpness of image edges or cause undesirable streaks or image
density artifacts. A larger level of drop placement error may be
tolerable for the printing of certain images, such as text and line
graphics only, than is acceptable for printing an image having
grayscale. Methods of operating a liquid drop emitter that emits
drops at different velocities will be further discussed
hereinbelow.
Drop placement errors, for drops having different volumes due to
drop velocity variations, may be avoided by using methods of
operating liquid drop emitters that achieve a substantially uniform
drop velocity. It has been found by the inventors of the present
inventions that the drop velocity of emitted drops having different
volumes may be made substantially constant by adjusting both the
time duration of the heat pulse, .tau..sub.p, and the applied
power, P, to achieve different amounts of pulse energy input,
E.
FIG. 12 shows experimental data 252 for drop volume emitted as a
function of input energy applied using a pulse time duration
.tau..sub.p and input power P adjusted to achieve a substantially
constant drop velocity of 8 m/sec. The data plotted in FIG. 12 were
collected for a representative drop emitter filled with water and
configured as illustrated in FIGS. 3 and 4. The drop emitter used
was similar to that used for the data reported in FIG. 11. The
cantilevered element 20 length L was 90 .mu.m; the width of the
rectangular portion of the cantilever and the diameter of the
semi-circular free end 28 both 30 .mu.m; the nozzle 30 diameter was
14 .mu.m; and the resistance of a heater resistor 27 formed in a
deflector layer 24 was 26 ohms. Individual data points are marked
by dots along plot 252. Individual data points are also labeled
with the applied heat pulse duration .tau..sub.p in microseconds
(.mu.s) and the applied power P in watts (W).
The experimental data reported in FIG. 12, as well as other data
collected by the inventors of the present inventions, show that it
is necessary to adjust the input power, as well as the total input
energy, in order to achieve a specific target drop velocity,
v.sub.d0, when generating drops having substantially different
volumes. It has been found experimentally that the power P must be
reduced while lengthening the time duration of the heat pulse,
.tau..sub.p, to a longer value, in order to achieve a desired drop
volume increase, otherwise, the drop velocity will also increase.
In addition, a threshold energy for the emission of a smallest drop
is observed. The smallest volume drop that could be emitted at 8
m/sec in the experiments reported in FIG. 12 was a 2.6 pL drop
emitted by the application of 3.3 .mu.J of energy.
Some preferred methods of operating a liquid drop emitter having a
thermo-mechanical actuator according to the present inventions are
to cause the emission of drops having substantially different
volumes while having substantially the same velocity. The term
"substantially different volumes", when used herein, means that the
range of drop volumes emitted is at least 20%, that is, that the
largest drop emitted has at least 20% more volume than the smallest
drop emitted. The term "substantially the same velocity", when used
herein, means that the range of drop velocities is less that 20%,
that is, that the fastest drop emitted is no more than 20% faster
than the slowest drop emitted. These preferred methods of operation
are accomplished by selecting, for each drop volume to be emitted,
appropriate heat pulse parameters including the total energy, power
and pulse time duration. Higher values of the total input heat
energy E are selected to emit larger drops. Lower values of the
power P together with longer pulse time duration values .tau..sub.p
are also selected to emit larger drops at substantially the same
velocity.
The practice of the methods of operating liquid drop emitters
according to the present inventions is preferably combined with
certain features of the liquid drop emitter apparatus. Firstly, it
is believed that the range of drop volumes accessible by changing
the energy, power and pulse time duration values is enhanced if the
thermo-mechanical actuator is configured as a cantilevered element
having an arcuate free end that moves within a closely-spaced,
surrounding, arcuate liquid chamber portion. This preferred
configuration is generally illustrated by the plan views in FIGS.
3a and 3b. For such a configuration the movement of the free end 28
translates efficiently into moving the fluid behind the nozzle.
Leakage of fluid around the free end 28 via the clearance distance
13 represents a loss of energy efficiency by weakening the direct
proportionality between the amount of free end deflection and the
volume of fluid that is moved toward the nozzle to form a jet. An
arcuate shape minimizes the perimeter to area ratio of the free
end, hence minimizes the length of the fluid leakage path around
the free end. It has been found by the inventors of the present
inventions that an arc of 180 degrees or more is preferable to
minimize energy losses. Generally conforming the stationary arcuate
portions of the upper and lower liquid chambers to the arcuate
shape of the free end edge, and minimizing the clearance distance
therebetween further reduces the leakage path. It has been found by
the inventors of the present inventions that it is preferable to
form as small a clearance distance as is reliably possible and
preferably less than 3 microns.
Secondly, a cantilevered element thermo-mechanical actuator will
exhibit a damped resonant oscillation following an initial thermal
excitation pulse. Referring to FIGS. 4a-4c, cantilevered element 20
will quickly relax from the bent position illustrated in FIG. 4b as
elements 24 and 26 equilibrate in temperature, as heat is
transferred to the working fluid and substrate 10, and due to
mechanical restoring forces set up in elements 24 and 26. The
relaxing cantilevered clement 20 will over shoot the quiescent
state, FIG. 4a, and bend downwards as illustrated in FIG. 4c.
Cantilevered element 20 will continue to "ring" in a resonant
oscillatory motion until damping mechanisms, such as internal
friction and working fluid resistance, deplete and convert all
residual mechanical energy to heat.
If predictable drop volume and velocities are important for the
application, the damped resonant oscillation effects described
above must be considered in designing the operating method.
Directing drop emissions at arbitrary times during the resonant
oscillations may cause intended drop volumes and intended drop
velocities to vary unacceptably. The present inventive methods of
operating a liquid drop emitter preferably are carried out so as to
avoid complications arising from intrinsic damped resonant
oscillations of the cantilevered element. This is accomplished by
selecting all pulse time duration values to be less than
one-quarter cycle of the period of the fundamental resonant mode,
.tau..sub.R.
FIGS. 13 and 14 illustrate damped resonant oscillation of the free
end 28 of a cantilever element 20 moving in fundamental mode. FIG.
13 discloses experimental data for several parameter variations of
the general thermo-mechanical actuator configuration illustrated in
FIGS. 3a-4c. The table in FIG. 13 discloses the observed
fundamental resonant frequency, F, the period of the fundamental
resonance, .tau..sub.R, and the damping time constant, .tau..sub.D,
for several different configurations of the cantilevered element
length, L, width, W, and free end diameter, D. The damped resonant
behavior disclosed was measured with water as the working
fluid.
Free end displacement, y(L,t), is plotted in FIG. 14 as a function
of time, t, according to Equation 6:
where .tau..sub.R is the period of the fundamental resonant
oscillation mode and .tau..sub.D is the time constant of damping
factors. The maximum magnitude of displacement is normalized to
1.0. The time axis in FIG. 14 is divided in units of .tau..sub.R.
Curves 220, 222, and 224 show damped resonant oscillations all
having the same resonant period .tau..sub.R, but having damping
time constant .tau..sub.D =0.75 .tau..sub.R, 10 .tau..sub.R, and
1.25 .tau..sub.R, respectively. Curve 226 shows the exponential
damping portion of Equation 6 for the case of curve 224. Curve 228
illustrates the electrical pulse that activated the
thermo-mechanical activators initially. Activation pulse duration,
.tau..sub.p, should be less than one-quarter the resonant period,
i.e. .tau..sub.p <1/4.tau..sub.R, to avoid the situation of
contention between the natural spring recoil of the cantilevered
element and the thermo-mechanical force introduced by the input
heat energy pulse.
The geometrical parameters for cantilevered elements given in the
table of FIG. 13 are typical of liquid emitter devices that are
appropriate for high quality ink jet printing and other liquid drop
emitter applications utilizing drop volumes of approximately 10 pL
or less. The highest resonant frequency of these experimental
devices was found to be 74 kHz, having a period of 13.5 .mu.sec.
Consequently, it is preferred to operate such a liquid drop emitter
according to the present inventions by insuring that all input heat
pulses have a time duration of approximately 3 .mu.sec or less.
Further methods of operating a liquid drop emitter according to the
present inventions are implemented utilizing drops having
substantially different volumes and substantially different
velocities. For some applications, the errors that may arise in the
drop placement at a predetermined receiver location are acceptable
within certain limits. For example, in ink jet printing
applications it may be that the printing of "draft" quality images
will be acceptable even though all drops are not printed
substantially at the predetermined raster location. In a
microdosiometer application it may be required that metered drops
land within a sample catch area that is large enough to tolerate
some misplacement in the drop trajectory.
FIG. 15 illustrates the drop placement error that may be associated
with varying drop velocity. In FIG. 15 a cut-away portion of a
thermo-mechanically actuated drop emitter 110 is shown in side view
in two positions indicated as "J" and "K". The cut-away portion of
drop emitter 110 is drawn after FIG. 4b showing the moment of drop
emission. In position J, a first drop 52 having a first volume
V.sub.1d and an emission velocity v.sub.1d0 is emitted. In position
K, a second drop 54 having a second volume V.sub.2d and a second
emission velocity v.sub.2d0 is emitted. In the illustrated example,
first drop 52 is selected as a small volume drop and travels at a
slow velocity. Second drop 54 is selected as a substantially larger
volume drop, V.sub.2d >V.sub.1d, and travels at a substantially
faster velocity, v.sub.2d0 >v.sub.1d0.
First and second drops 52 and 54 are intended to land at certain
predetermined locations 502 on receiver or print plane 500. For
example, predetermined locations 502 are labeled (i-2), (i-1), (i),
. . . , (i+7), and indicated by small plus signs. In the case of an
ink jet printing application, predetermined locations 502 are
individual pixel raster positions along a single scan line. For the
example of FIG. 15, first drop 52 is intended to land on
predetermined location (i) and second drop 54 is intended to land
on predetermined location (i+6). The receiver or print plane 500 is
located a firing distance G.sub.p from the nozzle plane of drop
emitter 110. Drop emitter 110 is illustrated moving at a velocity
v.sub.c in a direction parallel to print plane 500, for example by
means of a printhead carriage.
Because drop emitter 110 is moving at a vector velocity v.sub.c
with respect to the predetermined locations 502 at print plane 500,
the trajectory of emitted drops will follow the direction of the
vector sum, v.sub.d total, of v.sub.c and the drop emission
velocity vector v.sub.d0, the velocity of a drop if the drop
emitter were at rest. Straight line trajectory 506 in FIG. 15
illustrates the flight path of first drop 52 along the direction of
v.sub.1d total. Straight line trajectory 510 in FIG. 15 illustrates
the flight path of second drop 54 along the direction of v.sub.2d
total. Dotted lines 504 and 508 in FIG. 15 indicate the position of
drop emitter 110 with respect to predetermined print plane
locations 502 at the moment of the emission of first drop 52 and
second drop 54, respectively.
First drop 52 is emitted when the nozzle of drop emitter 110 is
opposite a print plane location just past predetermined location
(i-1). Second drop 54 is emitted when the nozzle of drop emitter
110 is similarly opposite a print plane location just past
predetermined location (i+5). The emission of first drop 52 is
timed to occur just after passing predetermined location (i-1) so
that it will land on predetermined print plane location (i). The
emission of second drop 54 is similarly timed to occur just after
passing predetermined location (i+5) and is intended to, but does
not, fall on predetermined location (i+6), because it is traveling
too fast. Second drop 54 lands at a point on the receiver 500 in
between predetermined locations (i+5) and (i+6), an error distance
.delta.2 away from predetermined location (i+6).
Error distance .delta..sub.2 adversely affects the quality of
performance of the liquid drop emitter in a fashion depending on
the specific application. For example, in the case of an ink jet
printing application, misplacement of some of the print drops by a
distance .delta..sub.2 away from the intended pixel raster
positions may cause perceptible anomalies, defects, in the image.
For a microdosiometer application, the drop may fall outside of an
intended chemical analysis site, leading to a false chemical
measurement.
Some preferred embodiments of the present inventions include
methods of operating a liquid drop emitter to emit drops having
substantially different drop volumes and substantially different
velocities wherein the range of permitted velocities is
predetermined to bound the drop velocity related drop placement
errors. The range of permitted velocities may be different for
different applications or application modes. For example, in ink
jet printing, different image quality levels may allow different
levels of drop placement error, hence a different permitted range
of drop velocities.
Let v.sub.d max and v.sub.d min be the maximum and minimum
predetermined, permitted, drop velocities to bound the variation of
drop placement at the print plane below a predetermined maximum
error amount, .delta..sub.max. The following relationship governs
the permitted drop velocities: ##EQU4##
It is common that the minimum velocity permitted, v.sub.d min, is
selected in recognition of other drop misplacement error sources,
especially off-axis tugging on the liquid jet arising from wetting
anomalies and debris at the nozzle exit. For example, it may be the
case that these nozzle front face effects are of such magnitude
that a minimum drop velocity of 3-5 m/sec is necessary to bound
drop placement errors from these sources. The maximum permitted
velocity, v.sub.d max, may then be selected to satisfy above
Equation 7.
A representative example for an ink jet printing application is:
permitted maximum variation in drop placement .delta..sub.max +30
.mu.m; firing distance G.sub.p =1000 .mu.m; printhead carriage
velocity v.sub.c =0.25 m/sec; and v.sub.d min =4 m/sec. From
Equation 7, the permitted v.sub.d max is then: ##EQU5##
Given the parameters of this example and the drop emitter
performance for the experimental conditions disclosed in FIG. 11,
drops having volumes over the range of .about.3.1 pL to 4.1 pL, and
velocities of .about.4 m/sec. to 7.7 m/sec., could be selected for
use without incurring drop velocity induced placement errors in
excess of .about.30 .mu.m.
Methods of operation of liquid drop emitters that emit drops having
substantially different volumes have been disclosed wherein the
drop velocities are adjusted to be substantially equal by proper
selection of both the input power and the pulse time duration of
applied heat pulses. Other methods of operating have been disclosed
wherein a range of drop velocities is permitted, said range being
bounded by a predetermined permitted maximum drop placement error.
The inventors of the present inventions also comprehend that the
principles of these methods of operation may be combined to permit
a wider range of drop volumes to be used. That is, adjustment of
the power and time duration of activating input heat pulses may be
used to provide a wider range of drop volumes emitted at a narrowed
range of velocities, wherein the narrowed velocity range is
selected to satisfy above Equation 7.
FIGS. 16a and 16b illustrate input heat pulse parameters that might
be used to generate first and second drops as illustrated in FIG.
15. In FIG. 16a a first heat pulse 260 is applied having a first
power P.sub.1, a first pulse time duration .tau..sub.p1, and first
energy E.sub.1 =P.sub.1.tau..sub.p1 to cause the emission of a
small drop 52. A second heat pulse 262 is applied having a second
power P.sub.2, a second pulse time duration .tau..sub.p2 and second
energy E.sub.2 =P.sub.2.tau..sub.p2 to cause the emission of a
large drop 54. In the example of FIG. 16a, the power and pulse time
duration parameters are adjusted to provide both the energy levels
to generate large and small drops, E.sub.2 >E.sub.1, and the
adjustments of pulse power and pulse time duration necessary to
maintain a substantially constant drop velocity, i.e., .tau..sub.p2
>.tau..sub.p1, P.sub.2 <P.sub.1, and v.sub.1 =v.sub.2.
The time axes in FIGS. 16a and 16b are drawn in units of
.tau..sub.R, the fundamental resonant period of a thermo-mechanical
actuator. This has been done to further emphasize that the heat
pulse time durations used are preferably less than 1/4.tau..sub.R.
First and second drop firing pulses 260 and 262 are initiated by a
clock signal 264, which is illustrated to have a period,
.tau..sub.C =4 .tau..sub.R. In an ink jet printing application
clock signal 264 is preferably synchronized to the movement of the
printhead relative to predetermined pixel locations, rasters, at
the print plane by some spatial encoding means. In the example of
FIGS. 16a and 16b, the drop firing pulses are initiated at a time
.about.1/4.tau..sub.R following the low-to-high transition of clock
signal 264. The low-to-high clock signal transition of clock signal
264 is a clock period start which may be used to time-reference
events within a clock period. For the example of FIG. 16a wherein
the drop velocities are substantially equal, the first and second
drops will follow trajectories that take them to predetermined
pixel locations at the print plane.
In FIG. 16b a first heat pulse 266 is applied having a power
P.sub.0, a first pulse time duration .tau..sub.p1 and first energy
E.sub.1 =P.sub.0.tau..sub.p1 to cause the emission of a small drop
52. A second heat pulse 268 is applied having also a power P.sub.0,
a second pulse time duration .tau..sub.p2 and second energy E.sub.2
=P.sub.0.tau..sub.p2 to cause the emission of a large drop 54. In
the example of FIG. 16b, pulse time duration parameters are
adjusted to provide the energy levels to generate large and small
drops, E.sub.2 >E.sub.1. However a same power level, P.sub.0, is
used, causing large drop 54 to be emitted at a higher velocity than
small drop 52, v.sub.2 >v.sub.1. Consequently, large drop 54
will arrive more quickly at the print plane and will be misplaced
by a placement error distance as illustrated in FIG. 15.
Alternate preferred methods of operating liquid drop emitters to
emit drops of substantially different volumes at substantially
different velocities may be carried out by adjusting the time of
application of activating heat pulses within a clock signal period.
That is, in order to compensate for the quicker travel time to the
print plane of faster drops, the heat pulse application may be
delayed relative to that of a slower drop. Especially for high
quality ink jet printing applications, it is important that each
print drop arrive at a predetermined location on the print plane. A
clock signal, synchronized to the printhead-receiver motion, may be
used to manage the timing of applied heat pulses, introducing an
appropriate amount of time delay to synchronize the arrival of
different velocity drops at the intended predetermined locations on
the receiver.
An appropriate amount of time delay may be introduced to
synchronize the arrival of drops at predetermined locations on the
receiver by associating a time delay factor, t.sub.d, with other
heat pulse parameters, power and pulse time duration, used to
generate a selected drop volume. For example, in the approach
illustrated in FIG. 16b, wherein different drop volumes are
generated using a constant pulse power and different pulse duration
times, a time delay quantity is associated with each pulse time
duration. Longer heat pulse durations will generate larger and
faster drops and have larger associated time delay factors.
A preferred method of operation utilizing time delay factors is
illustrated in FIG. 17. The method disclosed in FIG. 17 is similar
to the method illustrated by FIG. 16b except that a unique time
delay factor is associated with each applied heat pulse. Heat pulse
270 in FIG. 17 generates a small first drop 52. Heat pulse 270 is
initiated after a delay time, t.sub.1.about.0.25 .tau..sub.R,
following a low-to-high transition, the clock period start, of
clock signal 264. Time delay t.sub.1 is selected so that first
small drop 52 will arrive at a first intended raster position on
the receiver.
Heat pulse 272 in FIG. 17 generates a large second drop 54 that
will be traveling at a substantially higher velocity than first
small drop 52, as has been previously discussed. Heat pulse 272 is
initiated after a larger time delay, t.sub.2.about.1.15
.tau..sub.R, following a next clock period start. The larger time
delay, t.sub.2, is calculated to compensate for the shorter transit
time from drop emitter to receiver of second large drop 54 relative
to first small drop 52. Large second drop 54 will arrive at a
second raster position, adjacent to the first in the example of
FIG. 17. The second drop placement error that will occur in the
example method of operating of FIG. 16b is removed by the use of
the larger time delay t.sub.2 in the method according to FIG.
17.
An alternate preferred method of providing time delay compensation
to synchronize the arrival of drops having different velocities at
predetermined locations in the print plane is illustrated by FIG.
18. For these preferred methods a clock signal 294 is divided into
a number of sub-clocks 296 that provide a number of drop emission
trigger edges within each clock period. For the example illustrated
in FIG. 18, sub-clock signal 296 provides eight high-to-low
transitions per clock period, which may be used as eight trigger
times, tr.sub.1 to tr.sub.8. The subordinate trigger edges are
sometimes referred to as "phases" of the clock signal. While
illustrated as equally spaced in FIG. 18, some number of trigger
edges may be provided at non-equal time spacings within the clock
period.
In the alternate preferred method of operating a liquid drop
emitter illustrated in FIG. 18, each drop volume that is to be
emitted is associated with one of the available trigger edges. In
FIG. 18, first drop heat pulse 290 is associated with trigger edge
tr.sub.1 and second drop heat pulse 292 is associated with trigger
edge tr.sub.3. In the example of FIG. 18, the total clock period,
.tau..sub.c, is divided into eight equal parts by sub-clock 296 and
the trigger edges are chosen to be the high-to-low transitions
rather than a low-to-high edge as is used for the clock period
start. Each drop volume choice is associated with the trigger edge
that will result in the least drop placement error due to each drop
velocity.
Comparing the methods of operating illustrated in FIG. 17 to that
of FIG. 18 it may be seen that they are nearly the same. The second
drop is emitted after a delay of 1.25 .tau..sub.R following the
second clock period start in the method of FIG. 18 whereas it is
emitted after a time delay of 1.15 .tau..sub.R in the method of
FIG. 17. The method of FIG. 17, wherein a particular time delay is
associated with each drop volume, can result in the smaller drop
placement errors than the method of FIG. 18 which is limited to
choosing a "closest appropriate" trigger edge. However a finer
structure of trigger edges may be created to further minimize the
error in having to select from a finite set of delay times.
The methods of FIG. 18 may also be implemented by generating a
finite set of sub-clock trigger edges to accompany a finite set of
emitted drop volumes. For example, a system might be configured to
emit three discrete drop volumes, each drop size having an
associated specific velocity and optimum delay time. A sub-clock is
then constructed to provide three trigger edges that occur at the
optimum delay times. Such a system would operate as if the signal
clock had three phases, one for each drop size. Image data which
directs that a given pixel location should be printed with one of
the three drops sizes, or none, could then be organized into three
binary drop command files, drop or no drop, one for each of the
three phases, and executed in time-interleaved fashion.
A potential advantage of the preferred methods of the present
inventions, which utilize drops having different velocities, is
that a variable drop volume system may be constructed and operated
using a constant power input source and other parameters managed
via various timing means. Such an approach may offer lower cost and
higher reliability hardware as compared to an approach in which the
input power must be finely adjusted on a drop-by-drop basis to
equalize drop velocities.
The foregoing description of the present inventions was primarily
directed at thermo-mechanical actuators having a laminated
construction comprised of a deflector layer and a top layer, that
is, a bi-layer device. However, the inventors of the present
inventions contemplate that any construction configuration of a
thermo-mechanical actuator that is useful in a liquid drop emitter
may be used in practicing the inventions. In particular,
thermo-mechanical actuators having multiple deflector layers may be
operated according to the methods of the present inventions, in a
fashion similar to the single deflector layer constructions
described in detail herein.
While much of the foregoing description was directed to the
configuration and operation of a single thermo-mechanical actuator
or liquid drop emitter, it should be understood that the present
invention is applicable to forming arrays and assemblies of
multiple drop emitter units. Also it should be understood that
thermo-mechanical actuator devices according to the present
invention may be fabricated concurrently with other electronic
components and circuits, or formed on the same substrate before or
after the fabrication of electronic components and circuits.
From the foregoing, it will be seen that this invention is one well
adapted to obtain all of the ends and objects. The foregoing
description of preferred embodiments of the invention has been
presented for purposes of illustration and description. It is not
intended to be exhaustive or to limit the invention to the precise
form disclosed. Modification and variations are possible and will
be recognized by one skilled in the art in light of the above
teachings. Such additional embodiments fall within the spirit and
scope of the appended claims.
Parts List 10 device microelectronic substrate 11 upper liquid
chamber 12 lower liquid chamber 13 clearance gap between
thermo-mechanical actuator and arcuate liquid chamber walls 14
liquid chamber wall edge at cantilever anchor 15 thermo-mechanical
actuator 16 lower liquid chamber arcuate wall portion 17 anchor
portion of thermo-mechanical actuator 18 clearance opening removed
in passivation layer 22 19 side edges of the moveable cantilevered
element 20 cantilevered element of a thermo-mechanical actuator 22
lower passivation layer 24 deflector layer 26 top layer 28
cantilevered element free end 29 patterned sacrificial layer
material 30 nozzle 31 planar upper surface of the sacrificial layer
material 33 upper liquid chamber structure 34 arcuate edge of free
end 28 35 openings in passivation layer 22 for liquid refill
pathway 36 upper liquid chamber arcuate wall portion 38 planar
surface of upper liquid chamber structure 33 having nozzle 30 42
electrical input pad 44 electrical input pad 50 liquid drop 52
small volume drop 54 large volume drop 60 working fluid 80 support
structure 100 ink jet printhead 110 drop emitter unit 200
electrical pulse source 300 controller 400 image data source 500
receiver or print plane 502 print raster positions
* * * * *